VARIATION IN HUMANS By Desiree Williams

Mutations:  Mutations are A source of variation, not THE only source.  Mutations cause a change in D.N.A.  Mutations take place for three reasons. 1. To many codones, 2. Not enough codones, 3. Or out of order codones.  Mutations can be beneficial, but could also cause cancer.

Environment:  Environment also effects DNA, because the animals sometimes need to adapt to be more fit for their environment, So natural selection will occur.  Adapting : When an organism changes to better survive in its environment.  Fit: More likely to survive in its environment.  Natural selection is when the cells chose the most beneficial trait for survival.

Sexual Reproduction:  Sexual reproduction takes place, in meiosis.  Consists of germ, haploid, or sex cells. For the female, its eggs. For the male, its sperm.  You obtain 23 chromosomes from your mother, 23 from your father. Making there be 46 chromosomes in each human cell.  Obtaining traits from both mother, and father.

Chromosomes:  Chromosomes are DNA wrapped around protein with base pairs connecting.  An allele is a version of a gene.  Summatic cells: All cells but sex. Ex. Skin cells, hair cells, brain cells.  Summatic cells do NOT share chromosomes in the same way as germ cells.

Homologous:  Homologous: almost same chromosomes. With same set of genes but different versions.  Genotype: Versions of genes.  Phenotype: Physical trait.  1 phenotype = multiple different genotypes.

Different Variations.  There are TONS of options of variation.  In every human we carry 2 to the 23d power of versions in human reproduction.  So when a male, and a female combine, that gives up 2 to the 46 th power of variations within one couples reproduction.  DNA Recombination: Is when DNA crosses over between parents, which can increase variety even more.

The options are endless